A cross-site scripting flaw in the PayPal website allows a phishing attack to masquerade as a genuine PayPal login page with a valid security certificate, according to security researchers.

No word on a fix - yet

A cross-site scripting flaw in the PayPal website allows a phishing attack to masquerade as a genuine PayPal login page with a valid security certificate, according to security researchers.

Fraudsters are exploiting the flaw to harvest personal details, including PayPal logins and credit card details, according to staff at Netcraft, an internet services company in Bath. The PayPal site, owned by eBay, allows users to make online payments to one another, charged to their credit cards. Login credentials for the service are a prized target of fraudsters.

The attack works by tricking PayPal members into following a maliciously crafted link to a secure page on PayPal's site. Anyone thinking to check the site's security certificate at this point will see that it is a valid 256bit certificate belonging to the site, Netcraft employee Paul Mutton wrote in the company's blog today.

However, the URL exploits a flaw in PayPal's site that allows the fraudsters to inject some of their own code into the page that is returned, he wrote. In this case, the result is a warning that the user's account may have been compromised, and that they "will now be redirected to Resolution Center".

The page to which they are redirected asks for their PayPal account details - but thanks to the cross-site scripting flaw in the PayPal site, and the data injected into the URL by the fraudsters, the page is no longer on the PayPal site. Instead, the page steals the log-in details and sends them to the fraudsters' server, then prompts the user for other personal information, Mutton said.

The web server harvesting the personal details is hosted in Korea, Mutton said.

The cross-site scripting technique makes the phishing attempt difficult to detect, said Mike Prettejohn, also of Netcraft.

If the malicious link arrived by email, then "there would be clues in the mail that it's not genuine", he said. "It's a technique chosen by fraudsters because it is hard to spot."

Although there could be benign uses of cross-site scripting to transfer data between sites, the technique has an inherent security risk, Prettejohn said. "I don't think people would intentionally use it," he said.

"If somebody knows there's a cross-site scripting opportunity on their site, the right thing to do would be to fix it," he said.